The present invention relates to coordinated multi-point (CoMP) joint transmission (JT) in orthogonal frequency division multiple access (OFDMA) for a wireless communications system and more particularly to feedback and scheduling for CoMP JT in OFDMA.
Coordinated multi-point (CoMP) transmission, being standardized in Third Generation Partnership Project Long Term Evolution Advanced (3GPP LTE-Advanced), allows multi-cell cooperative processing to mitigate inter-cell interference (ICI) and the system to operate at higher effective signal-to-interference-plus-noise ratios (SINRs). Joint transmission (JT) CoMP transmission increases the user throughput especially cell edge users by jointly coordinating the transmission or receptions of user signals from multiple cooperating transmission points (TP).
The benefits of JT CoMP come at the cost of increased radio feedback and backhaul overhead. In addition, CoMP JT performance highly depends on the scheduling algorithms.
We proposes efficient feedback schemes with reduced signaling overhead and efficient scheduling algorithm. Based on the proposed feedback and scheduling, CoMP JT achieves significant cell-edge throughput gain over single cell transmission at the cost of much reduced feedback overhead and backhaul overhead.
There are some related works [1]-[5] in this field. Existing feedback [1] involves very high feedback overhead. The CoMP JT scheduling proposed in [2] involves high complexity due to the iterative design. The performance of the scheduling is not guaranteed with a suboptimal solution.    [1] S. Brueck, L. Zhao, J. Giese, and M. Amin, “Centralized scheduling for joint transmission coordinated multi-point in lte-advanced,” in Smart Antennas (WSA), 2010 International ITG Workshop on, February 2010, pp. 177-184.    [2] L. Thiele, V. Jungnickel, and T. Haustein, “Interference management for future cellular ofdma systems using coordinated multi-point transmission,” IEICE Transactions on Communications, vol. E93-B, no. 12, pp. 3228-3237, 2010.    [3] Coordinated multi-point operation for LTE physical layer aspects (Release 11), 3GPP Std. 3GPP TR 36.819, Rev. 11.0, 2011.    [4] LG Electronics, Motorola Mobility, et, al “Proposal for UE receiver assumption in CoMP simulations, 3GPP TSG-RAN WG1 R1-110586, 2011.    [5] Further advancements for E-UTRA physical layer aspects, 3GPP Std. 3GPP TR 36.814, Rev. 9.0, 2010.
In [1] and [2], the CoMP JT scheduling algorithm either applies greedy suboptimal scheme or involves iterative scheme, which has very complexity without a performance guarantee. [3] defines the CoMP feedback for JT, in which coherent phase difference information is considered. [5] defines the CQI/PMI/RI feedback format without giving the method to compute them.
We propose and investigate different feedback schemes with lower signaling overhead such as non-coherent JT and pre-scheduling CoMP user equipment (UE) fallback (PSCUF). With non-coherent JT, no phase adjustment feedback is needed for joint transmission. With PSCUF, a scheme dynamically allowing a CoMP UE to skip CoMP feedback and fallback to single cell transmission is enabled to reduce feedback overhead and maintain the throughput advantage of JT. Based on the proposed feedback option, we develop an optimal scheduling algorithm to achieve CoMP gain at a lower complexity.